A council has shared more than 1,000 people's email addresses in a data breach.
West Berkshire Council sent a leisure survey on Friday to 1,107 recipients who could all see each other's email addresses.
The council said it has reported the incident to data protection watchdog the Information Commissioner's Office (ICO).
The ICO said anyone with concerns about their data can report it to them.
In a statement, the council said: "On 25 October, the council was made aware of an incident by which a large number of service users were copied into an email containing a survey about leisure centres.
"This led to each recipient being able to see one another's email addresses."
The council later sent a second email to its service users saying: "We're really sorry that your email address was shared in this way."
It said a member of staff had inserted addresses into the wrong field when composing the email.
The ICO said it would not be commenting on the incident.